ABSORPTION OF RAIN AND DEW BY THE FOLIAGE-LEAVES. 225 into a mouldering mass. But as soon as they perish other new air-roots, covered with golden-brown velvet, make their appearance and take their place. These aerial roots never reach the ground or adhere to any substratum, so that their hairs cannot contract an organic connection with a solid body. It is consequently also irapossible in this case for the root-hairs to draw raoisture frora the soil in the capacity of absorption-cells. These root-hairs, however, are scarcely ever in a position to take up even the atraospheric deposits. The various species of Philodendron and the other epiphytes referred to, have large leaves which cover the air-roots hanging from the stem like urabrellas, and every tree-fern also bears at the top of its stem a tuft of great fronds, which prevents falling rain from wetting the aerial roots. Moreover, the very plants whose air-roots exhibit a velvety coating occur in woods where the tops of the trees arch over the ground in lofty domes, and forra a sheltering roof against deposits from the atmosphere. On the other hand, the air within these forests is saturated with aqueous vapour, and it is certain that the velvety roots have the power of condensing vapour, and that the root-hairs instantly suck up the condensed water and convey it to the deeper-lying layers of ceUs. The truth of this has been established by the results of repeated experiments. Thus, air-roots of the tree-fern Todea barbata, after being transferred frora raoderately damp air into a chamber full of vapour, condensed and absorbed in the space of twenty-four hours water amounting to 6'4 per cent of their weight. There is, therefore, no doubt that water raay be acquired in this way also by plants, even though the ipstances may not be very nuraerous. All plants in which this kind of water-absorption has been hitherto observed grow in places where the air is very moist the whole year round, and where there is also no risk of the temperature falHng below freezing- point. Under other conditions, especially in places where the air is periodicaUy very dry, these plants would not be able to survive; for, although they possess organs for the condensation and absorption of water, they have no raeans of protec¬ tion against the desiccation of these organs. ABSOEPTION OF EAIN AND DEW BY THE FOLIAGE-LEAVES. The idea that plants absorb with their roots such water as they require is so intimately associated with our whole conception of plant-life, that this process is commonly adduced for the purpose of analogies of the most various kinds, and one looks upon the water-absorption effected by aerial roots in the manner just described really as a thing to be expected, notwithstanding the fact that in this case, as the above account shows, the phenomenon is not so simple as is usuaUy supposed. We now tum to the consideration of land-plants. If the leaves of plants cultivated in pots become flaccid, water is poured as quickly as possible upon the dry soil with a view of supplying the roots which raraify in it with moisture. Nor does the result fail to be produced. In a short time the foliage becomes fresh and elastic again, the roots having discharged their function. Even in the open air, it is especiaUy VOL. L 15